Since I’m not a geologist I don’t claim to know what the inorganic constituents of Onion Mountain are. For that I defer to my associate, Dr. Anton Wroblewski, who refers to the underlying substrates of the Bluff Creek area as “silica-rich”. From an e-mail I received from Dr. Wroblewski:

Hi Matt,

Short answer: Absolutely, road construction would strip away all the topsoil and organics, leaving the pulverized bedrock (in the case of the Bluff Creek area, a dry, silica-rich dust).

Previously a number of my test casts had been made in volcanic ash (pumice) which I understand to be a mixture of aluminium and silicon oxides. But how would straight silicon dioxide (silica) test? On December 19, 2006 I purchased 20 pounds of silica from Seattle Pottery Supply:

I understand the “106” designation refers to how fine the powder is. Wearing rubber gloves I compacted a featureless foot shape into 10 pounds of silica and smoothed it with a polyethylene sheet.

I mixed plaster of Paris into cold water and poured the slurry into the test track:

I pulled the test cast about 45 minutes after pouring the cement and let it cure overnight before removing the remaining lightly adhered silica. I recorded the pertinent data onto the dorsal surface with a Sharpie permanent marker:

A variety of desiccation ridges appeared on the resulting cast. In addition, a number of furrows appeared, abutted by desiccation ridges:

This furrow appears just posterior to what would be the “ball” of the foot, and resembles the texture seen on CA-19 9cm anterior of the heel:

Compare to the band of ridges 9cm anterior of the heel on CA-19:

The pronounced furrow near the heel on the silica test cast is a strong match for a similar feature seen on CA-20:

And perhaps the most telling match of all; a band of ridges on the side of the silica test cast:

Compare with the texture that is claimed to be “Bigfoot’s dermal ridges”:

Frankly I was surprised at how closely the test cast textures matched the textures on CA-19, I didn’t expect this. But it should demonstrate beyond doubt that the spontaneous desiccation ridges are not dependent on one particular substrate, and have been demonstrated to occur in multiple purified and natural substrates.